Robert Foley <[email protected]> writes:
> On Mon, 18 Nov 2019 at 07:22, Alex Bennée <[email protected]> wrote: >> >> >> > + if (logfile) { >> > + qemu_flockfile(logfile->fd); >> > + return logfile->fd; >> > + } else { >> > + rcu_read_unlock(); >> >> As qemu_log_lock() and unlock should be paired we can drop the unlock >> here and do an unconditional unlock bellow even if a null fd is passed. >> >> Otherwise: >> >> Reviewed-by: Alex Bennée <[email protected]> >> > Sounds reasonable. It sounds like we should change it to be something > like this. > > static inline FILE *qemu_log_lock(void) > { > QemuLogFile *logfile; > rcu_read_lock(); > logfile = atomic_rcu_read(&qemu_logfile); > if (logfile) { > qemu_flockfile(logfile->fd); > return logfile->fd; > } > rcu_read_unlock(); > return NULL; > } > I will make the changes. No I mean as you have to call qemu_log_unlock() you can to the unlock there. You have to hold the lock over the usage of the resource: static inline FILE *qemu_log_lock(void) { QemuLogFile *logfile; rcu_read_lock(); logfile = atomic_rcu_read(&qemu_logfile); if (logfile) { qemu_flockfile(logfile->fd); return logfile->fd; } else { return NULL; } } static inline void qemu_log_unlock(FILE *fd) { if (fd) { qemu_funlockfile(fd); } rcu_read_unlock(); } > > Thanks, > -Rob > On Mon, 18 Nov 2019 at 07:22, Alex Bennée <[email protected]> wrote: >> >> >> Robert Foley <[email protected]> writes: >> >> > This now allows changing the logfile while logging is active, >> > and also solves the issue of a seg fault while changing the logfile. >> > >> > Any read access to the qemu_logfile handle will use >> > the rcu_read_lock()/unlock() around the use of the handle. >> > To fetch the handle we will use atomic_rcu_read(). >> > We also in many cases do a check for validity of the >> > logfile handle before using it to deal with the case where the >> > file is closed and set to NULL. >> > >> > The cases where we write to the qemu_logfile will use atomic_rcu_set(). >> > Writers will also use call_rcu() with a newly added qemu_logfile_free >> > function for freeing/closing when readers have finished. >> > >> > Signed-off-by: Robert Foley <[email protected]> >> > --- >> > v2 >> > - No specific changes, just merging in cleanup changes in >> > qemu_set_log(). >> > --- >> > v1 >> > - Changes for review comments. >> > - Minor changes to definition of QemuLogFile. >> > - Changed qemu_log_separate() to fix unbalanced and >> > remove qemu_log_enabled() check. >> > - changed qemu_log_lock() to include else. >> > - make qemu_logfile_free static. >> > - use g_assert(logfile) in qemu_logfile_free. >> > - Relocated unlock out of if/else in qemu_log_close(), and >> > in qemu_set_log(). >> > --- >> > include/qemu/log.h | 42 +++++++++++++++++++++++---- >> > util/log.c | 72 ++++++++++++++++++++++++++++++++-------------- >> > include/exec/log.h | 33 ++++++++++++++++++--- >> > tcg/tcg.c | 12 ++++++-- >> > 4 files changed, 126 insertions(+), 33 deletions(-) >> > >> > diff --git a/include/qemu/log.h b/include/qemu/log.h >> > index a7c5b01571..528e1f9dd7 100644 >> > --- a/include/qemu/log.h >> > +++ b/include/qemu/log.h >> > @@ -3,9 +3,16 @@ >> > >> > /* A small part of this API is split into its own header */ >> > #include "qemu/log-for-trace.h" >> > +#include "qemu/rcu.h" >> > + >> > +typedef struct QemuLogFile { >> > + struct rcu_head rcu; >> > + FILE *fd; >> > +} QemuLogFile; >> > >> > /* Private global variable, don't use */ >> > -extern FILE *qemu_logfile; >> > +extern QemuLogFile *qemu_logfile; >> > + >> > >> > /* >> > * The new API: >> > @@ -25,7 +32,16 @@ static inline bool qemu_log_enabled(void) >> > */ >> > static inline bool qemu_log_separate(void) >> > { >> > - return qemu_logfile != NULL && qemu_logfile != stderr; >> > + QemuLogFile *logfile; >> > + bool res = false; >> > + >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile && logfile->fd != stderr) { >> > + res = true; >> > + } >> > + rcu_read_unlock(); >> > + return res; >> > } >> > >> > #define CPU_LOG_TB_OUT_ASM (1 << 0) >> > @@ -55,14 +71,23 @@ static inline bool qemu_log_separate(void) >> > >> > static inline FILE *qemu_log_lock(void) >> > { >> > - qemu_flockfile(qemu_logfile); >> > - return logfile->fd; >> > + QemuLogFile *logfile; >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + qemu_flockfile(logfile->fd); >> > + return logfile->fd; >> > + } else { >> > + rcu_read_unlock(); >> >> As qemu_log_lock() and unlock should be paired we can drop the unlock >> here and do an unconditional unlock bellow even if a null fd is passed. >> >> Otherwise: >> >> Reviewed-by: Alex Bennée <[email protected]> >> >> > + return NULL; >> > + } >> > } >> > >> > static inline void qemu_log_unlock(FILE *fd) >> > { >> > if (fd) { >> > qemu_funlockfile(fd); >> > + rcu_read_unlock(); >> > } >> > } >> > >> > @@ -73,9 +98,14 @@ static inline void qemu_log_unlock(FILE *fd) >> > static inline void GCC_FMT_ATTR(1, 0) >> > qemu_log_vprintf(const char *fmt, va_list va) >> > { >> > - if (qemu_logfile) { >> > - vfprintf(qemu_logfile, fmt, va); >> > + QemuLogFile *logfile; >> > + >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + vfprintf(logfile->fd, fmt, va); >> > } >> > + rcu_read_unlock(); >> > } >> > >> > /* log only if a bit is set on the current loglevel mask: >> > diff --git a/util/log.c b/util/log.c >> > index 91ebb5c924..9f9b6b74b7 100644 >> > --- a/util/log.c >> > +++ b/util/log.c >> > @@ -28,7 +28,7 @@ >> > >> > static char *logfilename; >> > static QemuMutex qemu_logfile_mutex; >> > -FILE *qemu_logfile; >> > +QemuLogFile *qemu_logfile; >> > int qemu_loglevel; >> > static int log_append = 0; >> > static GArray *debug_regions; >> > @@ -37,10 +37,14 @@ static GArray *debug_regions; >> > int qemu_log(const char *fmt, ...) >> > { >> > int ret = 0; >> > - if (qemu_logfile) { >> > + QemuLogFile *logfile; >> > + >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > va_list ap; >> > va_start(ap, fmt); >> > - ret = vfprintf(qemu_logfile, fmt, ap); >> > + ret = vfprintf(logfile->fd, fmt, ap); >> > va_end(ap); >> > >> > /* Don't pass back error results. */ >> > @@ -48,6 +52,7 @@ int qemu_log(const char *fmt, ...) >> > ret = 0; >> > } >> > } >> > + rcu_read_unlock(); >> > return ret; >> > } >> > >> > @@ -56,12 +61,24 @@ static void __attribute__((__constructor__)) >> > qemu_logfile_init(void) >> > qemu_mutex_init(&qemu_logfile_mutex); >> > } >> > >> > +static void qemu_logfile_free(QemuLogFile *logfile) >> > +{ >> > + g_assert(logfile); >> > + >> > + if (logfile->fd != stderr) { >> > + fclose(logfile->fd); >> > + } >> > + g_free(logfile); >> > +} >> > + >> > static bool log_uses_own_buffers; >> > >> > /* enable or disable low levels log */ >> > void qemu_set_log(int log_flags) >> > { >> > bool need_to_open_file = false; >> > + QemuLogFile *logfile; >> > + >> > qemu_loglevel = log_flags; >> > #ifdef CONFIG_TRACE_LOG >> > qemu_loglevel |= LOG_TRACE; >> > @@ -80,43 +97,47 @@ void qemu_set_log(int log_flags) >> > g_assert(qemu_logfile_mutex.initialized); >> > qemu_mutex_lock(&qemu_logfile_mutex); >> > if (qemu_logfile && !need_to_open_file) { >> > - qemu_mutex_unlock(&qemu_logfile_mutex); >> > - qemu_log_close(); >> > + logfile = qemu_logfile; >> > + atomic_rcu_set(&qemu_logfile, NULL); >> > + call_rcu(logfile, qemu_logfile_free, rcu); >> > } else if (!qemu_logfile && need_to_open_file) { >> > + logfile = g_new0(QemuLogFile, 1); >> > if (logfilename) { >> > - qemu_logfile = fopen(logfilename, log_append ? "a" : "w"); >> > - if (!qemu_logfile) { >> > + logfile->fd = fopen(logfilename, log_append ? "a" : "w"); >> > + if (!logfile->fd) { >> > + g_free(logfile); >> > perror(logfilename); >> > _exit(1); >> > } >> > /* In case we are a daemon redirect stderr to logfile */ >> > if (is_daemonized()) { >> > - dup2(fileno(qemu_logfile), STDERR_FILENO); >> > - fclose(qemu_logfile); >> > + dup2(fileno(logfile->fd), STDERR_FILENO); >> > + fclose(logfile->fd); >> > /* This will skip closing logfile in qemu_log_close() */ >> > - qemu_logfile = stderr; >> > + logfile->fd = stderr; >> > } >> > } else { >> > /* Default to stderr if no log file specified */ >> > assert(!is_daemonized()); >> > - qemu_logfile = stderr; >> > + logfile->fd = stderr; >> > } >> > /* must avoid mmap() usage of glibc by setting a buffer "by hand" >> > */ >> > if (log_uses_own_buffers) { >> > static char logfile_buf[4096]; >> > >> > - setvbuf(qemu_logfile, logfile_buf, _IOLBF, >> > sizeof(logfile_buf)); >> > + setvbuf(logfile->fd, logfile_buf, _IOLBF, >> > sizeof(logfile_buf)); >> > } else { >> > #if defined(_WIN32) >> > /* Win32 doesn't support line-buffering, so use unbuffered >> > output. */ >> > - setvbuf(qemu_logfile, NULL, _IONBF, 0); >> > + setvbuf(logfile->fd, NULL, _IONBF, 0); >> > #else >> > - setvbuf(qemu_logfile, NULL, _IOLBF, 0); >> > + setvbuf(logfile->fd, NULL, _IOLBF, 0); >> > #endif >> > log_append = 1; >> > } >> > - qemu_mutex_unlock(&qemu_logfile_mutex); >> > + atomic_rcu_set(&qemu_logfile, logfile); >> > } >> > + qemu_mutex_unlock(&qemu_logfile_mutex); >> > } >> > >> > void qemu_log_needs_buffers(void) >> > @@ -245,19 +266,28 @@ out: >> > /* fflush() the log file */ >> > void qemu_log_flush(void) >> > { >> > - fflush(qemu_logfile); >> > + QemuLogFile *logfile; >> > + >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + fflush(logfile->fd); >> > + } >> > + rcu_read_unlock(); >> > } >> > >> > /* Close the log file */ >> > void qemu_log_close(void) >> > { >> > + QemuLogFile *logfile; >> > + >> > g_assert(qemu_logfile_mutex.initialized); >> > qemu_mutex_lock(&qemu_logfile_mutex); >> > - if (qemu_logfile) { >> > - if (qemu_logfile != stderr) { >> > - fclose(qemu_logfile); >> > - } >> > - qemu_logfile = NULL; >> > + logfile = qemu_logfile; >> > + >> > + if (logfile) { >> > + atomic_rcu_set(&qemu_logfile, NULL); >> > + call_rcu(logfile, qemu_logfile_free, rcu); >> > } >> > qemu_mutex_unlock(&qemu_logfile_mutex); >> > } >> > diff --git a/include/exec/log.h b/include/exec/log.h >> > index e2cfd436e6..9bd1e4aa20 100644 >> > --- a/include/exec/log.h >> > +++ b/include/exec/log.h >> > @@ -15,8 +15,15 @@ >> > */ >> > static inline void log_cpu_state(CPUState *cpu, int flags) >> > { >> > + QemuLogFile *logfile; >> > + >> > if (qemu_log_enabled()) { >> > - cpu_dump_state(cpu, qemu_logfile, flags); >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + cpu_dump_state(cpu, logfile->fd, flags); >> > + } >> > + rcu_read_unlock(); >> > } >> > } >> > >> > @@ -40,19 +47,37 @@ static inline void log_cpu_state_mask(int mask, >> > CPUState *cpu, int flags) >> > static inline void log_target_disas(CPUState *cpu, target_ulong start, >> > target_ulong len) >> > { >> > - target_disas(qemu_logfile, cpu, start, len); >> > + QemuLogFile *logfile; >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + target_disas(logfile->fd, cpu, start, len); >> > + } >> > + rcu_read_unlock(); >> > } >> > >> > static inline void log_disas(void *code, unsigned long size) >> > { >> > - disas(qemu_logfile, code, size); >> > + QemuLogFile *logfile; >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + disas(logfile->fd, code, size); >> > + } >> > + rcu_read_unlock(); >> > } >> > >> > #if defined(CONFIG_USER_ONLY) >> > /* page_dump() output to the log file: */ >> > static inline void log_page_dump(void) >> > { >> > - page_dump(qemu_logfile); >> > + QemuLogFile *logfile; >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + page_dump(logfile->fd); >> > + } >> > + rcu_read_unlock(); >> > } >> > #endif >> > #endif >> > diff --git a/tcg/tcg.c b/tcg/tcg.c >> > index 0511266d85..4f616ba38b 100644 >> > --- a/tcg/tcg.c >> > +++ b/tcg/tcg.c >> > @@ -2114,9 +2114,17 @@ static void tcg_dump_ops(TCGContext *s, bool >> > have_prefs) >> > } >> > >> > if (have_prefs || op->life) { >> > - for (; col < 40; ++col) { >> > - putc(' ', qemu_logfile); >> > + >> > + QemuLogFile *logfile; >> > + >> > + rcu_read_lock(); >> > + logfile = atomic_rcu_read(&qemu_logfile); >> > + if (logfile) { >> > + for (; col < 40; ++col) { >> > + putc(' ', logfile->fd); >> > + } >> > } >> > + rcu_read_unlock(); >> > } >> > >> > if (op->life) { >> >> >> -- >> Alex Bennée -- Alex Bennée
